In life in general there is frequently found the necessity for heating the contents of a barrel or tank or some other such object with a nonplaner surface. These objects may be located in a place subject to the ravages of the outdoors and the associated elements or they may be indoors and subject to cleaning spray or they may be in an area which contains or has a possibility of containing explosive gases. A practical and safe method to apply heat is to utilise a flexible electric heating pad fastened to the object. There are a number of such systems available and they do heat objects as required.
These systems in general include a heating element embedded between two flexible insulators, a ground shield to provide mechanical and grounding protection for the heater, a ground conductor connected to the ground shield and power conductors connected to the heating element, thermostatic control, a junction box in which terminations are made between the conductors and the power cord and a method by which the unit may be attached to the nonplaner surface.
Some of the systems have junction boxes which are bonded to the flexible heater and permanently seal the terminations between the conductors and the power cord and some have junction boxes which are mechanically attached to the flexible heater but do not provide a waterproof seal to the terminations and some have the junction box in a remote location from the connection between the ground conductor and the ground shield and the connection between the power conductors and the heating element. There follows a list of problems associated with these types of heating systems when utilized for heating objects subject to the ravages of the outdoors and the associated elements or indoors and subject to cleaning spray or in an area which contains or has a possibility of containing explosive gases.
For some industrial applications it is a requirement of certification agencies that electric heaters have a power cord which is replaceable in case of damage during use. In order to replace the power cord the termination between the power conductors and the power cord must not be permanently sealed and must be accessible thus necessitating the use of an accessible junction box. In addition the junction box must be sealed sufficiently or have inherent characteristics so as to prevent moisture or explosive gases from entering it. The problems include the difficulty of excluding moisture or explosive gases from the area of the connection between the ground shield and the ground conductor and between the heating element and the power conductors, the difficulty of preventing mechanical stress on the connection between the ground shield and the ground conductor and between the heating element and the power conductors, the difficulty of excluding moisture or explosive gases from the area of the termination between the conductors and the power cord, the difficulty of excluding moisture or explosive gases from the thermostat, the difficulty of maintaining access to the area of the termination between the conductors and the power cord, the difficulty of securing the junction box to the heater.